I convince people not to do this by making it potentially cost them: get out of the habit or end up double charged some day. Not true for the majority of ecommerce sites that handle doubled requests sensibly, but there's one poorly coded site out there just waiting to blow their bank account out.
Have you ever watched users try to interact with the web, their phone, and their desktop?
Many do not differentiate, and why should they have to? They all should be built using intuitive, unambiguous paradigms.